The Earth Science Picture of the Day (EPOD) highlights the diverse processes and phenomena which shape our planet and our lives. EPOD will collect and archive photos, imagery, graphics, and artwork with short explanatory captions and links exemplifying features within the Earth system. The community is invited to contribute digital imagery, short captions and relevant links.

Raindrop Distribution

The above photographic composite of rain water droplets sticking on various hydrophobic plant surfaces, following a downpour, indicates wide differences in size and shapes. It was taken in Siena, Tuscany, Italy. Raindrops can vary considerably in diameter, ranging from about 0.5 mm to 6.35 mm. They typically fall at a speed of about 8 to 32 km/h, hitting plant surfaces with a time of contact in the order of 3 milliseconds. The wax-like outer layer of a plant leaf produces a non-wetting interface that repels water and causes drops to bounce off the surface. This phenomenon is so common that it usually goes unnoticed. The basic physics governing the dynamics of water droplets is complex. However, understanding these events in detail could lead to the possibility of controlling them. For example, ensuring that herbicides and pesticides destined for the plants don't bounce off and contaminate the soil and public water supplies. In addition, preventing water raindrops from sticking to the surface of your car windscreen during a downpour would improve vision and thus safety. Perhaps, in the future, the natural strategy of plants to repel water droplets could be applied to car windows.